Our research objective is to synthesize and fully characterize new types of metal-thiolate complexes for the purpose of obtaining fundamental information about the structural, spectroscopic and reactivity properties of proteins containing metal-cysteine interactions. The metal-cysteine ligation mode occurs in a wide range of metalloproteins. We intend to prepare synthetic analogs for a number of metal-thiolate containing proteins; in particular those proteins which contain: iron (the iron-sulfur proteins), copper (blue copper and cytochrome c oxidase), zinc (alcohol dehydrogenase, aspartate transcarbamylase and metallothionein), cadmium (metallothionein) and molybdenum (xanthine oxidase and dehydrogenase, aldehyde oxidase, sulfite oxidase and nitrate reductase). Moreover, a number of metals (including cobalt, nickle, cadmium, iron and copper) have been incorporated into these proteins as spectroscopic probes. Chemico-physical studies of these model compounds will be used to achieve a fundamental understanding of the relationship between spectroscopic properties and the structural and electronic features of the metal center. In addition, the spectroscopic parameters determined from a variety of metal-thiolate model compounds should be useful to biochemists in their efforts to identify different types of metal-cysteine coordination modes.